Unexpectedly fast transfer of positron-emittable artificial substrate into N-terminus of peptide/protein mediated by wild-type L/F-tRNA-protein transferase

Facile and Efficient Chemoenzymatic Semisynthesis of Fc-Fusion Compounds for Half-Life Extension of Pharmaceutical Components

The formation of Fc-fusions, in which biologically active molecules and the Fc fragment of antibodies are linked to each other, is one of the most efficient and successful half-life extension technologies to be developed and applied to peptide and protein pharmaceuticals thus far. Fc-fusion compounds are generally produced by recombinant methods. However, these cannot be applied to artificial middle molecules, such as peptides with non-natural amino acids, unnatural cyclic peptides, or pharmaceutical oligonucleotides. Here, we developed a simple, efficient, semisynthetic method for Fc-fusion production involving our previously developed enzymatic N-terminal extension reaction (i.e., NEXT-A reaction) and strain-promoted azide-alkyne cycloaddition, achieving quantitative conversion and high selectivity for the N-terminus of the Fc protein. An Fc-fusion compound prepared by this method showed comparable biological activity to that of the original peptide and a long-circulating plasma half-life. Thus, the proposed method is potentially applicable for the conjugation of a wide range of pharmaceutical components.

Perspectives and Insights into the Competition for Aminoacyl-tRNAs between the Translational Machinery and for tRNA Dependent Non-Ribosomal Peptide Bond Formation

Aminoacyl-tRNA protein transferases catalyze the transfer of amino acids from aminoacyl-tRNAs to polypeptide substrates. Different forms of these enzymes are found in the different kingdoms of life and have been identified to be central to a wide variety of cellular processes. L/F-transferase is the sole member of this class of enzyme found in Escherichia coli and catalyzes the transfer of leucine to the N-termini of proteins which result in the targeted degradation of the modified protein. Recent investigations on the tRNA specificity of L/F-transferase have revealed the unique recognition nucleotides for a preferred Leu-tRNA^Leu isoacceptor substrate. In addition to discussing this tRNA selectivity by L/F-transferase, we present and discuss a hypothesis and its implications regarding the apparent competition for this aminoacyl-tRNA between L/F-transferase and the translational machinery. Our discussion reveals a hypothetical involvement of the bacterial stringent response that occurs upon amino acid limitation as a potential cellular event that may reduce this competition and provide the opportunity for L/F-transferase to readily increase its access to the pool of aminoacylated tRNA substrates.